Just weeks after homegrown Muslim terrorists attacked London, the British people affirmed their support for multiculturalism, according to a MORI poll for the BBC. It was heartening evidence that Britons have overcome the racism of their colonial past and learned to appreciate the carnival of color I joined when I took the Tube across central London shortly after the bombings.

But multiculturalism means more than better food and brighter festivals. It involves the trickier challenge of building community out of disparate populations with disparate traditions and disparate beliefs, all the while preserving and celebrating those disparities. That's what European countries are having a hard time coming to grips with -- and understandably so, because multiculturalism swept into Europe before its member countries had developed a philosophy to accommodate it. British author and psychologist Kenan Malik puts it more starkly. "Multiculturalism as lived experience enriches our lives," he has written. "But multiculturalism as a political ideology has helped create a tribal Britain with no political or moral centre."

Unlike America, where every new immigrant can make America more American (as President Bush once argued), and where the founding philosophy and civic rituals were designed to create a citizenry out of the masses, European countries were established less deliberately -- largely on shared traditions, shared languages, shared histories and even shared genes.

Recognizing the resulting deficit in civic ritual and the potential for a repeat of the kind of racial unrest that shook northern England four years ago, Britain's Labor government has been making a belated effort to engender "common values and a sense of belonging." Just 18 months ago, Britain held its first naturalization ceremony, in the London borough of Brent, publicly marking the moment the foreigner crossed the threshold to become a Briton. There, each citizen-in-the-making officially pledged "loyalty to the United Kingdom" and to "respect its rights and freedoms" as well as to "fulfil my duties and obligations as a British citizen."

More recently, just a few weeks before the bombings, the Home Office announced that, from November onward, prospective Britons will have to take a citizenship test to demonstrate some knowledge of the nation's past, an appreciation of its institutions, and an awareness of its customs and laws. The test is the product of a government-appointed panel led by the political theorist Bernard Crick, who has indulged in much soul-searching about just what it takes to be a modern multicultural Brit.

Is it important to know exactly what goes into the Christmas pud, for example, or how to get a new telephone installed? Should a prospective Briton understand how to use the National Health Service or know what happened in 1066 and all that?

This uneasy balance of cultural, practical and historical know-how has been widely ridiculed, but Crick's work represents an important if imperfect step toward establishing what it means to belong. And the need for heightened civic awareness isn't only among newcomers. Citizenship classes have already become a compulsory part of the school curriculum. For my niece in Cheshire, "citizenship" meant learning about the United Nations' Universal Declaration of Human Rights (though when I spoke to her she didn't know what that had to do with being British); and for one of my nephews, it meant working on a building for children in the Cornish town where he grew up.

Now there is talk of some sort of coming-of-age citizenship ceremony for 18-year-olds, as well as a national "Citizenship Day" to celebrate the bonds of Britishness (probably without parades and sparklers, which might be, uh, a bit too brash).

Old hat, Americans (or Australians) may say. But it's an essential new approach to belonging that is being developed in the Old World in response to what the New World knows well -- mass migration. Other European countries would do well to emulate it. After the bombings, Tony Blair said that "staying here carries with it a duty. That duty is to share and support the values that sustain the British way of life." The trouble is, those values have never been enshrined in the Old World's founding philosophy, leaving only the anything-goes message of multiculturalism.

Or almost anything. In its handbook for newcomers, "Life in the United Kingdom: A Journey to Citizenship," Crick's panel offers handy hints on how to act like a true Brit: In a pub, for example, "If you spill a stranger's drink by accident, it is good manners (and prudent) to offer to buy another."

The very hardest thing to understand, you see, may be the British sense of humor.

The writer, a dual citizen of Britain and the United States, is an assistant editor of Outlook. Her e-mail address is sellersf@washpost.com.